We will continue to investigate the properties of ribulose bisphophate (RuBP) carboxylase from Thiocapsa, Micrococcus denitrificans and Pseudomonas oxalaticus. Included will be studies of quaternary and active-site structure. Included in the studies of enzymes from these three sources will be detailed investigations of the kinetic response to CO2 to differentiate between activation by CO2 and the utilization of CO2 via catalysis. We will also undertake a study of the hybridization of subunits of RuBP carboxylase from one source with those from another source. Finally we may undertake efforts to mutagenize Rhodospirillum rubrum and select for mutants for elevated RuBP carboxylase/oxygenase ratios. These mutants should exhibit less inhibition of growth on CO2 by oxygen. BIBLIOGRAPHIC REFERENCES: K. Purohit, and B.A. McFadden, The Quaternary Structure and Oxygenase Activity of D-Ribulose-1,5-Bisphosphate Carboxylase from Hydrogenomonase eutropha, J. Bacteriol. 129, 415 (1977). B.A. McFadden, The Structure, Function and Evolution of Microbial Ribulose Bisphosphate Carboxylase, Proceedings of the Second International Symposium on Photosynthetic Prokaryotes, pp. 190-192 (1977).